37,253 research outputs found
System maintains constant penetration during fusion welding
Servo system senses variations in fusion welding process, and adjusts the control parameters to compensate for them. The system assumes a correlation between uniform weld penetration and temperature gradients near the molten puddle. It senses weld properties and makes adjustments to travel speed and weld current
Towards a wave-extraction method for numerical relativity. V. Extracting the Weyl scalars in the quasi-Kinnersley tetrad from spatial data
We extract the Weyl scalars and in the quasi-Kinnersley
tetrad by finding initially the (gauge--, tetrad--, and
background--independent) transverse quasi-Kinnersley frame. This step still
leaves two undetermined degrees of freedom: the ratio , and
one of the phases (the product and the {\em sum} of
the phases are determined by the so-called BB radiation scalar). The residual
symmetry ("spin/boost") can be removed by gauge fixing of spin coefficients in
two steps: First, we break the boost symmetry by requiring that
corresponds to a global constant mass parameter that equals the ADM mass (or,
equivalently in perturbation theory, that or equal their values in
the no-radiation limits), thus determining the two moduli of the Weyl scalars
, while leaving their phases as yet undetermined. Second,
we break the spin symmetry by requiring that the ratio gives the
expected polarization state for the gravitational waves, thus determining the
phases. Our method of gauge fixing--specifically its second step--is
appropriate for cases for which the Weyl curvature is purely electric. Applying
this method to Misner and Brill--Lindquist data, we explicitly find the Weyl
scalars and perturbatively in the quasi-Kinnersley tetrad.Comment: 13 page
CFD modelling of buoyancy-driven natural ventilation opposed by wind
This paper presents CFD simulations of natural displacement ventilation airflows in which the buoyancy force produced by a heat source is opposed by a wind force. Cases investigated focus on windbuoyancy force relationships for which a two-layer stratification is maintained. CFD predictions of the position of the interface separating the two layers and the change in reduced gravity (temperature
difference) between them are compared with the analytical work and salt-bath measurements of Hunt and Linden (2000, 2005). Comparisons are good with only minor discrepancies in the interface position and a small under-prediction of the upper layer reduced gravity
Use of steepest descent and various approximations for efficient computation of minimum noise aircraft landing trajectories
The following areas related to landing trajectory optimization research were discussed: (1) programming and modifying the steepest descent optimization procedure, (2) successfully iterating toward the optimum for a four-mile trajectory, (3) beginning optimization runs for a twenty-mile trajectory, and (4) adapt wind tunnel data for computer usage. Other related areas were discussed in detail in the two previous annual reports
Optimization and sensitivity studies of flight-path trajectories
The optimization of landing trajectories of the Boeing 737 is presented. The primary factor considered was the noise delivered to the population residing near an air terminal but passenger comfort, fuel consumption and time elapsed during the maneuver were also considered. A digital simulation of the aircraft, a noise model and a passenger comfort model, was completed. The digital simulation was made more efficient time-wise. A population model for an urban area was developed and the noise model was integrated into the population model. A steepest descent optimization algorithm was programmed. Some constant glide slope trajectories into an urban Airport were simulated and evaluated with respect to the performance index, and their ground track plotted
Quasi-circular Orbits for Spinning Binary Black Holes
Using an effective potential method we examine binary black holes where the
individual holes carry spin. We trace out sequences of quasi-circular orbits
and locate the innermost stable circular orbit as a function of spin. At large
separations, the sequences of quasi-circular orbits match well with
post-Newtonian expansions, although a clear signature of the simplifying
assumption of conformal flatness is seen. The position of the ISCO is found to
be strongly dependent on the magnitude of the spin on each black hole. At close
separations of the holes, the effective potential method breaks down. In all
cases where an ISCO could be determined, we found that an apparent horizon
encompassing both holes forms for separations well inside the ISCO.
Nevertheless, we argue that the formation of a common horizon is still
associated with the breakdown of the effective potential method.Comment: 13 pages, 10 figures, submitted to PR
Design and development of a water vapor electrolysis unit
Design and development of water vapor electrolysis unit for oxygen productio
The two-phase approximation for black hole collisions: Is it robust?
Recently Abrahams and Cook devised a method of estimating the total radiated
energy resulting from collisions of distant black holes by applying Newtonian
evolution to the holes up to the point where a common apparent horizon forms
around the two black holes and subsequently applying Schwarzschild perturbation
techniques . Despite the crudeness of their method, their results for the case
of head-on collisions were surprisingly accurate. Here we take advantage of the
simple radiated energy formula devised in the close-slow approximation for
black hole collisions to test how strongly the Abrahams-Cook result depends on
the choice of moment when the method of evolution switches over from Newtonian
to general relativistic evolution. We find that their result is robust, not
depending strongly on this choice.Comment: 4 pages, 3 figures, submitted to Classical and Quantum Gravit
Relativistic stars in differential rotation: bounds on the dragging rate and on the rotational energy
For general relativistic equilibrium stellar models (stationary axisymmetric
asymptotically flat and convection-free) with differential rotation, it is
shown that for a wide class of rotation laws the distribution of angular
velocity of the fluid has a sign, say "positive", and then both the dragging
rate and the angular momentum density are positive. In addition, the "mean
value" (with respect to an intrinsic density) of the dragging rate is shown to
be less than the mean value of the fluid angular velocity (in full general,
without having to restrict the rotation law, nor the uniformity in sign of the
fluid angular velocity); this inequality yields the positivity and an upper
bound of the total rotational energy.Comment: 23 pages, no figures, LaTeX. Submitted to J. Math. Phy
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